Background: Breast cancer is the second leading cause of cancer death among women in Iran. Considering the effect of this disease on the quality of life of affected women, the issue of this research is to identify the factors affecting the quality of life of this group of patients. Aims: This study was performed to describe quality of life in patients with breast cancer undergoing chemotherapy and its relationship with demographic characteristics and functionalities (physical, emotional, social, Cognitive and sexual) have been done. Method: The research method is descriptive and correlational. The sample included 116 women with breast cancer. Data were analyzed using stepwise regression. Results: Disturbance in social function (P<0.01) and intensity of pain (P<0.01) are the strongest predictors of quality of life in breast cancer patients. Also, there was a significant relationship between demographic variables such as age, parenthood, employment status and education with quality of life (P<0.05). Conclusions: In this sense, preserving function and social relationships and managing pain are effective in improving the quality of life of this group of patients.